Lens subluxation after plasmin and SF6 injections in rabbit eyes.

PURPOSE: To investigate the rate of lens subluxation following plasmin and/or SF6 injections in eyes, and whether a subsequent elevated level of vascular endothelial growth factor (VEGF) and vitreous tap would aggravate subluxation. METHODS: Four groups of rabbits were used. Group 1 received an intravitreal injection (IVI) of plasmin and SF6 in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF6 in the right eye; and group 4 received an IVI of balanced salt solution in the right eye. After treatment, IVIs of VEGF were given and vitreous tap was performed three times, followed by clinical observation of lens subluxation and scanning electronic microscope evaluation of the zonular fibers. RESULTS: After IVIs of plasmin and SF6, and VEGF and vitreous tap had been performed one to three times, lens subluxation was noted in 0%, 43%, 71%, 71%, and 86% of the eyes in group 1. After IVIs of plasmin, VEGF, and vitreous tap had been performed one to three times, lens subluxation was noted in 11%, 22%, 44%, 44%, and 67% of the eyes in group 2. The eyes in group 3 and 4 did not show signs of lens subluxation after VEGF IVIs and vitreous tap. Histology confirmed zonular fiber damage in the eyes treated with plasmin. CONCLUSIONS: The incidence of lens subluxation increased following plasmin injections in the eyes, and this was aggravated by the subsequent high VEGF level in the eyes and vitreous tapping. Zonular fibers were disrupted following plasmin treatment. These effects should be kept in mind when using plasmin enzymes in patients with vitreoretinal abnormalities.

Efficient vitreolysis by combining plasmin and sulfur hexafluoride injection in a preclinical study in rabbit eyes.

PURPOSE: To investigate the efficacy of plasmin and sulfur hexafluoride (SF(6)) on the vitreoretinal junction, as well as the long-term safety in the eye and effect on the recipient's general health after application in the eye. METHODS: The study design included four groups of rabbits with three animals in each group. Group 1 received an intravitreal injection (IVI) of plasmin and SF(6) in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF(6) in the right eye; and group 4 received an IVI of balanced salt solution in the right eye, which served as a normal control. Long-term safety (up to approximately three months) after plasmin and/or SF(6) injection was evaluated morphologically by clinical examination, histology, and immunohistochemistry, and functionally by electroretinograms (ERGs). General health evaluations after intravitreal injection included the assessment of weight gain, food intake, body temperature, and complete blood count analysis. RESULTS: Plasmin plus SF(6) injection resulted in complete posterior vitreous detachment (PVD), whereas plasmin or SF(6) injection alone resulted in only partial PVD. Balanced salt solution did not induce PVD. Eighty days after intravitreal injection, there were no major differences among the eyes of the three groups of animals compared with the normal control animals upon clinical evaluation, or regarding retinal morphology and ERGs. The lenses examined remained clear for up to 80 days following the intravitreal injection of plasmin plus SF(6), except one eye in the plasmin-treated group. ERGs decreased transiently one week after intravitreal injection in groups 1 through 3, but animals recovered fully to normal status afterward. General health was not affected after the injection of plasmin plus SF(6). CONCLUSIONS: Efficient vitreoretinal separation could be achieved, and an acceptable long-term safety profile was noted after plasmin plus SF(6) injection in the eye. No major ocular toxicity or systemic toxicity was found after the injection of plasmin plus SF(6). These results provide good support for the future clinical use of plasmin plus SF(6) for treatment of a variety of vitreoretinopathies.

Plasmin treatment accelerates vascular endothelial growth factor clearance from rabbit eyes.

PURPOSE: To investigate the clearance of vascular endothelial growth factor (VEGF) after the induction of posterior vitreous detachment by plasmin and/or SF(6). METHODS: The study design included four groups of rabbits: group 1 received an intravitreal injection of plasmin and SF(6) in the right eye, group 2 received an intravitreal injection of plasmin in the right eye, group 3 received an intravitreal injection of SF(6) in the right eye, and group 4 received an intravitreal injection of balanced salt solution in the right eye. Intravitreal injection of human VEGF (50 µL, 10 ng/µL) was performed in study eyes and control eyes 1 month after plasmin and/or SF(6) injection. Serum and vitreous samples were collected on days 1, 3, and 7 after VEGF injection to determine the serum and vitreous concentrations of VEGF. RESULTS: One day after VEGF injection, residual human VEGF concentration in the vitreous cavity was significantly lower in the plasmin- and SF(6)-treated eyes (group 1) and the plasmin-treated eyes (group 2) when compared with the control eyes (group 4) (P = 0.047 and 0.027, respectively). Three days after VEGF injection, the residual VEGF concentration in the vitreous cavity was still significantly lower in the plasmin- and SF(6)-treated eyes (group 1) when compared with the control eyes (group 4) (P = 0.025). CONCLUSIONS: Eyes treated with plasmin exhibit a more rapid clearance of exogenous VEGF than control eyes. This finding suggests a novel treatment for retinopathies associated with vitreous traction and VEGF elevation.

Long-term tolerability and serum concentration of bevacizumab (avastin) when injected in newborn rabbit eyes.

PURPOSE. To test the long-term effects and systemic exposure level after single or multiple bevacizumab (Avastin) intravitreal injections in newborn rabbit eyes. METHODS. Four groups of newborn New Zealand rabbits received a single intravitreal bevacizumab injection at a concentration of 1.25 mg/0.05 mL at the ages of 2 (group 1), 4 (group 2), 6 (group 3), and 12 (group 5) weeks. The other group of rabbits (group 4) received three consecutive injections of bevacizumab at a concentration of 1.25 mg/0.05 mL at weeks 2, 6, and 10. Eight days after injection, the serum concentration of bevacizumab was determined in groups 1, 2, 3, and 5. Morphologic and functional changes were evaluated 12 months after bevacizumab injection. RESULTS. Twelve months after either single or multiple intravitreal injections of bevacizumab, newborn rabbit eyes showed no significant differences compared with control eyes on examination with funduscopy, histopathology, or electroretinogram. The serum concentrations when the injections were performed at the ages of 2 (19.4 +/- 8.1 microg/mL) and 4 (10.2 +/- 2.3 microg/mL) weeks were significantly higher than the serum level detected when the injection was performed at 12 weeks of age (2.8 +/- 1.2 microg/mL, P = 0.02 and P = 0.024, respectively). CONCLUSIONS. After 1 year, single and three consecutive intravitreal injections of 1.25 mg bevacizumab in newborn rabbit eyes are well tolerated. Systemic exposure is higher when the injection is performed at an early age.